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Superconducting generator on the test stand

Compact design, low tower head mass and good transportability: The high-temperature superconducting generator, which was developed in the EcoSwing research project, is to be used in the next generation of multi-megawatt turbines. The practical feasibility of the concept is being verified in a test campaign on Fraunhofer IWES’ nacelle test rig and in a follow-up field test in a two-blade system in Denmark. Fraunhofer IWES experts can already attest to the concept's maturity test on the test stand: The functionality of the overall system has impressed under realistic loads on the rotor and grid side.

Less is sometimes more: 40 per cent lower weight and smaller dimensions than a comparable permanent magnet excited synchronous generator—these properties are only possible thanks to superconductivity, as only a fraction of the magnetically active material is required for the same power density as conventional generators. Since this technology has almost no resistance, the conductor’s cross-section can be drastically reduced—a promising alternative for the development of future wind turbine generations.

“In the ambitious EcoSwing project, we were the first in the world to take the application of superconducting technology to a new level. Tests under realistic conditions are crucial to mitigate uncertainty. The DyNaLab enables us to achieve reliable results under defined test conditions,” said Jesper Hansen, Senior Project Manager at Envision Energy.

The “EcoSwing” rotor consists of two parts thermally decoupled by a vacuum chamber. The part responsible for bearing and the mechanical connection of the generator rotor is operated at ambient temperatures; the electrical part of the generator rotor is designed for operation at cryogenic temperatures. This resulted in a special requirement profile for the test stand: The generator had to be cooled down to 30 K (around -240 degrees Celsius) via a closed loop gas cooling system. The integration of such a cooling system was implemented for the first time at the Fraunhofer IWES. It has proven to be very reliable.

As part of the “EcoSwing” project, the Fraunhofer IWES designed the mechanical adaptations required for a connection to the test stand and developed and integrated a highly accurate measurement system to record the extremely high torques. “Due to the special drive train concept, the generator is subjected to virtually no parasitic loads during turbine operation—this same situation also had to be ensured during test stand operation. To achieve this, the generator was aligned and mounted with a high degree of precision,” said Dipl.-Ing. Hans Kyling, IWES project leader for EcoSwing manager in the project, explaining the unique challenge.

At the same time, another prerequisite was essential: The generator had to be clamped in such a way that it could make an evasive movement when subjected to nominal load. The specific adaptation prevented constraining forces from acting on the test object and influencing the test data.

The test results indicate both a successful validation and a high functionality. The project partners are now eagerly awaiting the field campaign with a 3.6 MW Envision test turbine in Denmark. The generator, which has a diameter of only 4 meters, will be transported there by ship.

The project, which is funded by the European Union, will run until the end of February 2019. The next step—leading up to commercial application—is already being planned by the project partners.